The #8da4d3 notation is a Hexidecimal value representing the colors Red, Blue, and Green (That particular number is some shade of bluish-grey).  The first two letters are for the Red value, the second two letters are for the Green value, and the last two are for the Blue Value.  Each two characters represent a value from 0 to 255, in Hexidecimal format, giving you a total palette of 16777216 possible colors. 

For example:

#000000 = Black
#FFFFFF = White
#FF0000 = Red
#00FF00 = Green
#0000FF = Blue
#FFFF00 = Yellow
#800080 = Purple
Etc...

Some of the more common colors (like the ones I listed) have names associated with them, so you can just type in the name of the color instead of remember the Hexidecimal values.  Others, you will probably need to use a webpage design program that has a "Color Picker" just so you can figure out the exact hue you need.

Hope this helps...

For grabbing colors from other parts of the screen (webpages, apps, etc) I found Pixie by Nattyware to be a great small little app.